I play both Galaxy and Olympia (as I know R. Wallace does) and I think elements
from Galaxy could be used to cover the idea of a local economy, including food
production.

For those (few) of you who are unfamiar with Galaxy, each planet has a size and
a natural resource (NR) level. The size limits the total population that may be
supported by the planet. The NR is a factor that determines how much
production is gained by effort expended, ranging from (theoretically) 0 to 10.

If regions in Olympia were assigned sizes and NR it could:
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Identify the maximum number NPC-type commoners the area could support
Identify the current number NPC-type commoners in the area (for HIRE)
Identify the quality of the local market economy...

eg - a '1' market would have minimal markup
a '10' market would have tremendous inflation/markup
a '0.1' market would be flooded with goods and have sacrifice prices

This would make trading profitable! Buy 100 swords for 5 gold in Drass and
truck them to Kircarth where you sell them for 1000 gold = 995 gold profit!

Hokay, this needs more thought, but the idea of 'size' and NR levels for
regions could be the basis for an economy...